Tracer valve



May 31, 196@ R. Rosi-:BROOK TRACER VALVE 3 Sheets-Sheet l Filed OCT.. 29, 1956 INVENTOR. ROY @OSEROO/f R. RosEBRooK 2,938,702

TRACER VALVE 3 Sheecs-Sheefl 3 May 31, 1960 Filed oct. 29, 1956 mm mr Q wg m16@ ,4 rra/iwf K ilnited States TRACER VALVE Filed Oct. 29, 1956, Ser. No. 619,010

2 Claims. (Cl. 251-3) This invention relates to tracer mechanism, and more particularly to a tracer mechanism adapted for use with hydraulically operated duplicating devices wherein the tracer mechanism controls hydraulic motors for causing relative movements of a cutting tool and a work piece, in order to reproduce the shape of a template or pattern, or the like in the work piece.

An object of this invention is to provide a tracer valve capable of controlling the relative shifting of the work piece and cutting tool so that external force on these ele-` ments have less ability to override the tracer valve control. For example, in climb milling, the milling cutter tends to force the work piece and carriage to move, independently of the power supplied by the tracer valve.

vThe valve of this invention represses this override tendency. A related object is to provide a tracer valve which can provide a low feed rate without chattering.

Still another object of this invention is to provide a manifolded valve which provides both quick action and delicate control in a convenient and useful single valve structure.

It is well known that in milling operations which are powered by hydraulic means, and which have tracer valves for governing the hydraulic tlow, the forces exerted by a milling cutter, particularly in climb milling, s frequently sufficient to pull hydraulic uid into the pressure side of the cylinder. This results in a feed rate which isl higher than the rate which is established by the tracer valve.

lFurthermore, in tracer valves, rate controls must frequently be set so as to provide a minimum rate of feed. At this rate of speed, chattering often takes place, because the stylus opens the valve by only a very small amount to control movement at slow rates. A chattering of the valve frequently occurs because of latent instabilities in the system which become important when the valve is only slightly opened.

Conventional tracer valves are unable to cope with these problems, and when high power is used on the cutting tool, and low feed rates are used, low tolerances and poor finishes occasionally result. The tracer valve of this invention overcomes many of these problems.

This invention is carried out in combination with a tracer valve having a pivotally mounted stylus which has a tip for tracing along a template or pattern. The stylus is tilted so that the tip contacts a pattern or template. This tilting action shifts the spool of a spool valve to direct hydraulic iluid under pressure to hydraulic motors. The hydraulic motors shift the work piece and the cutting tool relative to each other, and the machinery moves s as to nullify the stylus movement by the templates forcing the stylus to resume a neutral position. The cutter is thereby caused to duplicate the contour of the template.

According to this invention, an adjustable restrictor valve is disposed in the hydraulic line between the tracer rate of dow of duid through said line.

arent O 2,935,7@2 Patented May 31, 1550 ICC -sides in an adjustable master restrictor valve-in the hydraulic line which supplies hydraulic uid under pressure to the tracer valve. This master restrictor valve provides a limitation on the relative shifting of the work piece and cutting tool which is independent of the stylus control. It tends to overcome the effects of cutting tool forces which tend to shift the work piece and cutting tool without reference to the tracer valve.

The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, of which:

Fig. l is a perspective View, partly in cutaway crosssection, and partly in schematic notation, of a tracer valve incorporating the invention;

Fig. 2 is a View, partly in cross-section, taken at line 2-2 of Fig. l; and

Fig. 3 is a View, partly in cross-section, taken at line 3--3 of Fig. 1.

In Fig. 1 there is shown a perspective view of a tracer valve 10 incorporating the invention. This valve is the control unit for shifting a cutting tool and a work piece relative to each other so as to duplicate the contour of a template or pattern. The relative shifting movement may be accomplished either by moving a work table which supports the work piece, or by moving the cutting tool itself, or by any combination of the two. The actual movement of the element which is to be shifted may conveniently be accomplished by hydraulic motors. A hydraulic cylinder and piston assembly is one well-known form of hydraulic motor.

The application of a tracer valve to a machine tool for this purpose is well-known. For a complete description of a machine tool which utilizes a tracer valve of this general type, reference may be had to my Patent Number 2,753,145, issued July 3, 1956.

The tracer valve has a body 11 with a depending hollow neck 12 beneath the body. A tracer stylus 13 is pivotally mounted in the neck. The stylus has a lower template-engaging tip 14 which extends below the lower end of the neck l2. A ba1l-like member 15 is incorporated at a medial point of the stylus, and serves as a pivotal mounting for the stylus. The stylus tip can be swung in any lateral direction, with the ball acting as a fulcrum.

There is no restriction on the direction in which the lower tip of the stylus can swing. The surrounding structure, of course, limits the extent of the total swing of the erse rate control which is described in detail in my aforesaid Patent Number 2,753,145. Reference may be had to this patent for further details. This traverse rate control does not form a part of this invention, and will not be discussed further herein.

A second ball-like member 20 is incorporated in the stylus on the opposite side of the rst ball-like member 15. A yoke 21 comprising two U-shaped members 22, 23 and a block 24, are fitted around the ball-like member 20. The U-shaped members are crossed and opposed relative to each other so as to contain the block within them. Holes 25 through Ithe block and the bights of the U-shaped members permit the stylus to passthrough the yoke. The second ball-like member 20 iits snugly within valve and the hydraulic motor for adjustably limiting the the block 24.

Tilting the stylus moves the second ball-like member ,the pressure groove trom' each other.

lthe X and Y components. of'thezniotion ,of vthe block.

This yoke mounting is morelfully vdisclosed intheaforesaid Patent Number 2,753,l45,:to which-referencemay be had for additional details, because the yoke mounting forms no part of this invention.

An X-axis spool valve 26 and a Y-axis spool valvew27 Vare placed at right angles Vto Veach other, and to the neutral (vertical) position of the stylus. V.Spool valve 26 comprises a cylindery 28 with a .pressure inlet port .29 and a pair of X axis outlet ports 3G, 31. Power cylindersupply ports 32, 33 also open into the.v cylinder 28. l

An X-axis spool34 is disposed inthe cylinder 28( so as to be axially slidable therein. The spool has a central peripheral pressure groove 35 whichis always in fluid communication with pressure inletV port 29. Peripheral exhaust grooves 36, 37 are located on opposite sides of These exhaust grooves are placed in fluid communication with X-axis outlet port 3i)- or31, when the spool is shifted .toward or away from the stylus, respectively.

A `rod 38 joins X-axis spool 34 to U-shaped member 22. The spool is thereby movably mounted to the second ball-like member'20 of the stylus through the yoke V21.

Y-axis spool `valve 27 comprises a cylinder 39 having t an axially slidable Y-axisy spool 40 therein. Spool 46is "joined to U-shapedmember 23 by a rod 41, andis thereby mounted to the second ball-like ymember 20 of the stylus through the yoke 21.

The Yaxis cylinder 39 has a pressure inlet port 42 and i a pair of outlet ports 43, 43a opening thereinto. Y-axis power cylinder supplypports 44, 45 also open into the cylinder.

The Y-axis spool has a central peripheral pressure groove 46 which isvalways inluid communication with inlet port 42. Peripheral exhaust grooves 47, 47a are locatedron opposite sides of the pressure groove from each other. These exhaust grooves are placed in fluid communication with outlet port 43a or 43 when the spool is shifted-toward or away from the stylus, respectively.

,Ap pump 48 withdraws and pressurizes hydraulic uid from a reservoir 49. The-,pressurized fluid is supplied to pressure inlet 50, which is controlled byv a master restrictor `'valve 51. `Masterrestrictor valve 51 will be described haust conduit 59 discharges into the reservoir 49.

The above-described conduits provide pressurized fluid to the spool valves, and scavenge exhausted fluid therefrom. It is'the function of the spool valves to direct the pressurized fluid to the hydraulicmotors which will cause the desired relative movement Lof the cutting tool vand Y workpiece. The spool valves l'also directV the exhausted, depressurized 'uid from the motors into the conduits which lead to the exhaust conduit'59. K

Motor )supply conduit 69 leads from -X-axis Vpower cylinder support port 32 'to one side of X-'axis'hydraulicl motor 61. Motor supply conduit 62 leads from X-axis motor cylinder supply port 33 yto a motor supply restrictor valve 63 which will be further described below. VMotor supply conduit 64 is the continuation'of conduit 621beyond the restrictor .valve 63, and connects V'toY the' other side of X-axis hydraulic motor 61.

Motor 'supply' conduit 565 leads` from Y-axispower cylinder supply port 45 to one side of Y-axis hydraulic motor 66. Motor supply conduit 67 leads from Y-axs power cylinder supply port 44 to a motor supply restrictor valve 68 which will he further described below. Motor supply conduit y69 is a continuation of conduit 67 beyond the restrictor valve 68, and connects to the other side of Y-laxis hydraulic motor66.

Y In the event that scavenging'of seeping hydraulic fluid is required, a bore 70 may be sunk into the valve body to `any/regions to .be scavenged. Vacuum -is applied at litting 71 to remove the uid. f

In accordance with common practice, the conduits in this tracer valve are formed by Ydrilling intersecting holes, some of which are plugged at the surface of the block 11. The ports in the cylinders comprise holes through sleeves which contain the cylinder. This is a well-known construction expedient for hydraulic valves.

v The mechanism of master restrictor valve `51, which is shown in detail in Fig. 2, will now be described. i It is V conveniently placed in a cylindrical bore 72 which passes through the body of the tracer valve. Cylindrical Yinserts 73, 74, 75, and a retainer 76, which form part of this Ivva-lve mechanism, are held in abutment by plugs 77 and Y78. Boss 79 on plug 77 acts las a limit stop forthe valve mechanism. Boss 80 on plug 78 acts as a base for parts 4jof thejvalve mechanism. Sleeve 81 is pressed into the tracer valve `body, and has a central bore which constitutes Y.cylinder 39; A u

Y A valvestemZ is slidably disposed within sleeve 74. A keyY 83 in the sleeve slides in a key'groo've 84 in the vv,stem to prevent the valvestem from rotating. A .boss

, 85 on the valvepstem is adapted to strike boss 79 at its farthest position to the left in Fig. 1.

The .valve stem 82 is provided with three Oring grooves `86, 87-and 88, which hold O rings 89, 90 and 91, respectively. 0 rings 89 and 9G are on opposite sides of conduit 52. O rings r90 and 91 are substantiallyon opposite sides of conduit 50. vHoles 92 and 93 are drilled through the side of insert 74 to continue conduits 50 and 52 respectively.

p Valve edge 94 at hole 92is adaptedv to beconta'cted by AOring 90 vto shut off llow between conduits 50 and V52.

y.A vse`ct`ion'95 of the stem adjacent to conduit 52 is turned down .to permitiuid toow from conduit 'to conduit 451152 when the O ring 90is unseated from edge 94.

i AI threaded sink 96 in the right hand end of the stem receives a threaded .rotatable adjustment screw 97. `screwhas a gear 9,8 attached thereto which' "acts as a ,collar to keep it from shifting longitudinally. 'The screw 50 passes 'through the insert 76 and the plug`78. It also proj'eizts through cover plate 99. Turning 'this adjustment screw therefore shiftsthe valve stem.

Y `A cylindrical stop 10) is iixed to the retainer 76. This stop 'surrounds the screw and limits movement of the stem to the right in Fig. 2. A coil spring 101 is opposed between retainer 76 and the valve stem for the purpose of eliminating backlash between the screw and stem, and also for biasing the screw to the left. This spring thereby "eliminates any looseness of t in the means for adjusting the `stern position.

y `In the event that it is desired to adjust the 'stem position at .a dilerent rate than is conveniently 'obtainable from simply `turning screw 97, a,second"'gear 102 canbe mounted to `shaft 163 as showntin Fig. 2. This .shaft 55 is `journaled ina sink 164.' Gear 102'has a vlarger radius than gear Y98 and is meshed thereto. If th'e'sh'aft 103 is A turned tov a given angle, screw 97 will be turnedthrough `a v.larger angle, but the 'amountvby which thel 'screw is movedz'canbe `closely determined Yfrom examining a dial (if provided) `on the shaft 103.

f 'Restrictor valves 63 and 68 r4are identical. Therefore only restrictor Valve 68 Vwill "be described in detail, it `'being lunderstood that `each of' ythese vvalvesjhas-correspending parts. 'With particularreference to',` Fig;l 3,

restrictor valve 68 is shown in -aicylindrical bore'l105-f` A moved to the right as shown in Fig. 1.

aeaavos spacer 106, insert 107, and spacer 108 :abut each other, and are held in firm abutment by a cover plate 109. Insert 107 has a hole 110 to continue conduit 67, and another hole 111 to continue conduit 69.

Valve stem 112 is slidably disposed within the inserts. Three O ring grooves 11251, 113 and 114 are provided on thestem, which hold O rings 115, 116 and 117, respectively. rings 115 and 116 are on opposite sides of conduit 67, and O rings 116 and 117 are substantially on opposite sides of conduit 69. The term valve seal is.

used interchangeably with the term O ring for O rings which are movable into contact with a valve seat to control iluid ow. A reduced-diameter section 118 of the stem between O rings 115 and 116 permits fluid flow between conduits 67 and 69.

A key 119 is fastened in insert 107. This key lits into a longitudinal keyway 120 in the stem and keeps the stem from rotating.

A threaded bore 121 in the end of the stem receives a threaded shaft 122, this shaft projecting through cover plate 109. A knurled collar 123 is pinned to the shaft in order to turn the shaft and also to pull on the stem.

A cylindrical limit stop 124 is xed to the cover plate 109. This limits movement of the stem to the right in Fig. 3. A coil spring 125 is placed between the stem and the cover plate to eliminate backlash in the threads, and to bias the stem to the left.

Valve edge 126 at holes 111 is so disposed that it may be contacted by O ring 116 to shut olf ow in either direction between conduits 67 and 69.

For convenience in disclosure, the shaft in restrictor valve numbered 122 in valve 68, is denoted by number 127 in restrictor valve 63 (see Fig. 1) and likewise, co1- lar 123 is denoted by number 128 in valve 63. With these exceptions, the structural elements of valves 63 and 68 are denoted by the same numbers. understood that restrictor valve 63 controls the flow between conduits 62 and 64, while valve 68 controls ow between conduits 67 and 69.

In operation this tracer valve is rst set up on the machine tool along with a template or pattern to be duplicated. A work piece and a cutting tool are adjusted in the same relative positions as the stylus and template. Then the cutting tool is rotated so that it will cut into the work piece and the tracer stylus is moved by hand over the surface of the pattern. ivoting of the stylus around the ball like member 15 moves the upper end of the stylus 13 in an opposite direction therefrom. This causes the second ball like member 20 to move in this opposite direction.

The yoke 21, against which the second ball like member 20 progresses, acts to resolve the movement of said second ball like member into its X and Y components. These components are transmitted by rods 3S and 31 to spools 34 and 40, respectively, of the X-axis and Y-axis spool valves 26 and 27. The movement of the spools and the valves causes the peripheral grooves in the spools to be placed into selective fluid communication with conduits leading to the hydraulic motors.

As a single example, assume that the spool 34 is It will be recalled that pressure in inlet port 29 is always in connection with the central 'peripheral pressure groove 35 on X axes spool 34. Movement of the spool in the aforesaid direction, causes this groove 35 to overlap both the pressure inlet port 29 and the power cylinder supply port 33, thereby supplying pressurized fluid to the restrictor valve 63, and through the restrictor valve to conduit 64 which is directly connnected to hydraulic motor 61.

This same movement of the spool 34 causes exhaust groove 36 to be brought into registration with power p cylinder supply port 32, which is in turn in communication with motor `supply conduit 60. The exhaust groove '36 lis also in registration with outlet port 30, and

It will be' thereby the motor supply conduit 60 is connected through manifold to exhaust conduit 59. The aforesaid valve adjustments and connections cause the piston in hydraulic motor 61 to be moved in the same direction as the tip of the stylus was moved. It is evident that this hydraulic motor may be used to shift either the workpiece or the cutting tool as desired. The reverse movement of spool 34 from that described above would cause the central peripheral pressure groove 35 to register with power supply port 32 thereby applying pressure to conduit 60, while exhaust groove 37 would be placed in registration with power cylinder supply port 33 and with outlet port 31, whereby the conduits 64 and 62 would discharge into manifold55 and thence through conduit 59 to the reservoir. It will be appreciated that these valve arrangements and connections will reverse the direction of motion of hydraulic motor 61.

Irrespective of which direction the stylus is moved with a component in the X-axis, hydraulic uid will pass in equal volume, through both conduits 60 and 64. One of these conduits will be connected to pressure and the other to reservoir, the particular connection depending on which way the stylus tip is moved. Evidently, the volume displaced from the low-pressure side of the piston must equal the volume introduced under pressure, because the cross-section of the cylinder in motor 61 is uniform. This relationship is strictly true when a double rod piston-cylinder combination, or a gear-type motor is used in which the volume change for a unitary move ment of the motor is the same in both directions. In the device illustrated, wherein the piston rod projects from only one side of the piston, it will be understood that a'slightly different volume of fluid is displaced in moving the piston the same distance in one direction than in the other. This effect is not particularly marked, inasmuch as the piston rod is of a considerably smaller diameter than the cylinder. The difference is usually of the order of about 5%. Whether or not the volumes are the same in either direction, it still remains true that the motor supply restrictor valve acts to restrict the rate of operation in either direction, regardless of the fact that it is physically connected only between conduits 62 and 64, and not in conduit 60.

The operation of the spool valve 27 to control flow through conduits 65 and 69 so as to operate hydraulic motor 66 are as just described for the X-axis spool valve 26, it being understood that spool valve 27 controls movement in the Y axis instead of the X axis. Restrictor valve 68 controls uid through conduits 65 and 69 in both directions of ow for motor 66 in the same manner as restrictor valve 63 controls uid for motor 61.

The mechanism and operation of restrictor valves 63 and 68 will be fully understood from reference to Fig. 3, wherein restrictor valve 68 is shown in detail. When it is desired to shut o movement in the Y-axis entirely independently of the movement of the stylus in the Y direction, the valve is closed by turning the knurled knob 123 counterclockwise when facing the right-hand side of the tracer valve as shown in Fig. 3 so as to turn the shaft and move the stem 112 to the left. This causes O ring 116 to make contact with valve edge 126, and also to pass beyond said edge, thereby shutting off flow between the conduits 67 and 69. Therefore, regardless of any movement of the stylus in the Y direction, no huid can iiow through either conduit 65 or 69, and hydraulic motor 66 will not operate. If it is desired to allow tiow through restrictor valves 68 at some regulated rate, the knurled nut is turned clockwise so as to move the stem 112 to the right in Fig. 3. This removes the O ring 116 from the valve edge 126 and permits uid to ow between conduits 67 and 69. It will be appreciated that the actual' valve restriction between said two conduits is between the stem structure to the left' of the 0 ring 113 and the valve edge. The 0 ring 116 makes `a'positive seal for shutolf, since the stem structure may Ypermit some slightleakage without the O ring.

" v'When the-stem is moved to' the right by the action-of 'fthe shaft,'then'educed-diameter section 118 of the valve stem is' inregistration with hole 111 to an extent deter- -mined'by the distance of movement of the-stem. 1A regulated flow vof fluid may pass through the restrictor valve under this condition.

ln the-.event -thatai-quick and unrestricted flow of. fluid 'through valve v68is desired, the knurled-knob 123 may be-pulled to the rightV Without turning the screw in its threads. This Ypulls the stem to the rightandopensthe valve. Thisf open 'condition will persist 'so vlong -as the knurled knob` is held Aagainst spring'125. When the knob Vis released, this spring `125 returns the Ystem to the position determined .by the: positioning of the shaft `122 relative to the stem 112. "This restrictorvalve therefore provides both a delicate adjustment by means of the -threaded joint relative to shaft 122' and stem '112, and also a quick traverse, wide-open valve condition obtained by pulling on the shaft, whereby therestn'ctor valve may .be quickly opened wide for high 'volume flow of tluid.

lt will be understood that 'the restrictorY valve 63 operates linthe same manner, 'knurled knob 128 being turned or pulled in the same manner as knurled knob 123, 'and for the same results in the control of motor 61.

The operation of master restrictor valve 51 WillV be described with particular reference to Fig. 2. This master restrictor valve is .disposed in the hydraulic supply line which supplies pressurized uid from the pump to spool 'valves 25 and 27. Therefore any restriction on'this master restrictor valve is effective in regulating the maximum rate of operation lof both of the hydraulic motors simultaneously. For that matter, the entire system may Vbe shut down by closing this master restrictor valve. Y

The master restrictor valve is adjusted by turning the screw 97, which positions the valve stem 82 inside the valve. lThe valve stern is axially slidable, andiskeyed against rotation by'key 83. When the stem is positioned f so that lthe ring 96 engages -the'valve edge 94, as shown in Fig. 2, fluid ow is shut off. When flow isdesired 'through the valve, the shaft 97 is turned clockwise to move the stern to the right, thereby withdrawing the O ring 90 from the valve edge 94, and also moving the portion of the stem which is to the left of `O'ring4 87 vpast the valve edge 94. This permits ow between convduits Slland S2. The rate of this flow is regulated by the YVextent of the opening between the valve stem land the valve edge 94. Cylindrical lstop 100 limits the movement of the valve stem to the right. Abutment of bosses 79 and 85 limits the movement of the valve stem to the left.

Turning the screw 97 gives a fairly tine adjustment of Vthe valve. For even closer adjustments, the shaft 103 may be turned so as to adjust the screw 97 through the gear train comprising gears 93 and 98.

The tracer valve providesv means for controlling the rate of movement of the hydraulic motors, which means are independent of the stylus control. For example, it is possible to provide for a greater rate of movement in one direction than another, even though the stylus displacementmay be the same. It is also possible to provide for ak gross movement in one axis at a time, which is a oo n-V venient feature when setting up a machine. This is done by simply pulling either' restrictor valve 63 or 68 out by the knobas appropriate, and displacing the stylus point.

The restrictor valves -63 and 63 are also useful in restraining the tendency of a machine to creep, particularly in climb milling, because they act as an adjusted orivlice to 'limit rate of fluid ow. The spool valves connected to the stylus can then be used as a close. regulated variableforice This feature reduces chattering in maychine installations.

AIt is frequently desired to exert an overall control on they rate of Itraverse -such that a maximum-rate may not beexceeded. 'For'this purpose themaster restrictor valve 51 isprovided, which limits the pressurefsupplyto both "pistons. Thismastersupply 'valve also prevents iluid from being drawn finto-the system from the pump l.be- 5 causel of for'ces'exerted by the cuttingtool, ina-manner similar to. that set forth in connectionv with valves 63 and -168. For'example,1if"a cutting tool-is operated witha powerof l0 H.P. vin climb milling,l l0 YHzP. is exerted :on the workpiece, tendingto move the Work table. This 10 Y'considerable power tends to draw'hydraulicfluid into the motor independently of the control position of the stylus, and may therefore result in poor tolerances on the comfpletedwork. By restricting the linward ow of tiuid -with restrictor valve"51,the' possibility of uid being drawn into the system is significantly reduced. This providesin etect,"a stabilizing means whereby a relativepositioning between the-workpiece and cutting tool is maintained by the hydraulic system until the said positionl is changed asa result `of stylus movement. It will be un- -derstood that restrictor valves'63 and 68 similarly repressed the tendency of the fluid to be drawn into the hydraulicmotorralong the axis of the spool valve with which `they are-associated. Y

This tracer valve provides a convenient valve which signiicantly speeds up machine operation, while increas` ing the accuracy of the work produced. It will be appreciated that all of the pressure supply lines, and all of the exhaust lines are' `manifolded,V so that hose connections areminimized. 'The Ycombination threaded and snap-res-trictor valves 63 and 68:are located directly on the tracel'r valve where the operator Vmust be lstationed anyway. These restrictor valves provide both coarse and nnerate adjustments 'for movement in the individual axes. The master restrictor valve, which is also located in the tracer '35 valve body 11, provides for closeadjustment of over-all valve rate.V l

This invention therefore provides a tracer valveY which sets up an inherently .more accurate and `reliablemachine tool control system. This invention is not -to be limited 40 to the embodiments shown in the drawing and Vdescribed in the description, which are given by way of example, and not by wayof limitation, but onlyr in accordance'with the accompanying claims.

I claim:

1. In a tracer :valve which .includes apair 'of spool valves whose position is adjustable by atracer stylus,V a pair of motor supply conduits .connected to each'of1said `spool valves, a pressure inlet to said tracer valvewhich supplies tluid under pressure for each of said spool valves,

said tracer valve having a pair of bores` therein, `the improvement comprising a pair of motor supply restrictor valves, one of said valves being disposed in each of said bores, said motor supply restrictor valves each comprising a valve seat, a valve stem within said bore, an"0 ring surrounding said valve stems so disposed andarranged as to make contact with said valve seat :in one position with the valve stem so as to shut off iluid ow through the motor supply conduit in which it is disposed in onepposition thereof, and to restrict uid ilow in some other Ypositions of said stern, and means for adjusting the axial position of said valve stem to adjust the amount of restriction to -iiuid ow comprisingmeans for restraining said valve stem against rotation, a threaded boredn said stem, a threaded shaft threadedly attachedZte said stem andprojecting-through the tracer valve, so as tobe axially slidabletherein, and knob means for turning and pulling said shaft, for 'enabling said valve to be slowly or rapidly opened, each one of the spool valvesbeing connected to an individual one of said motor supply restrictor valves, each motor supply restrictor valve being disposed in one of the motor supply conduits which is connected to its respective spool valve.

l2. In combination, a `tracer'valve including arpair'of spool valves adjustable vby a tracer stylus, a pair "of motor 7 5 supply conduits connected to' each of said spool valves, a

pressure inlet to said tracer valve, a master restrictor valve connected to said pressure inlet, two pressure supply conduits, each interconnecting a respective one of said spool valves to the master restrictor valve, and an exhaust conduit branching to each of said spool valves, the positions of the spool valves as determined by the tracer stylus adjusting the spool valves to regulate the rate and direction of uid ow through the motor supply conduits, two separate motor supply restrictor valves, each one of the spool valves being connected to an individual one of said motor supply restrictor valves, each motor restrictor valve being disposed in one of the motor supply conduits which is connected to its respective spool valve, said motor supply restrictor valves each comprising a valve seat, a valve stem within said bore, a valve seal on said valve stem so disposed and arranged as to make contact with said valve seat in one position of the valve stem so as to shut 0E uid ow through the motor supply conduit in which it is disposed in one position thereof, and to permit fluid flow in some other position thereof, each motor supply restrictor valve being independently actuable for selective control of its respective motor supply conduit, andmeans for adjusting the positioning of said valve stem to adjust the amount of restriction to uid ow through said valve comprising means for restraining said valve stem against rotation, a threaded bore in said stern, a threaded shaft threadedly attached Vto said stem and projecting from the tracer valve, and knob means for turning and pulling said shaft, for slowly or rapidly opening said motor supply restrictor valve, respectively, whereby the master restrictor valve controls ow through the pressure supply conduits, thereby restricting flow through both spool valves, and the motor supply restrictor valves each controls liow through an individual one of said spool valves.

References Cited in the file of this patent UNITED STATES PATENTS 2,157,240 Keel May 9, 1939 2,456,158 Tancred Dec. 14, 1948 2,585,328 Johnson Feb. 12, 1952 2,725,896 Barker Dec. 6, 1955 2,726,581 Roehm Dec. 13, 1955 

